The present invention relates to lighting devices and in particular to lighting devices that have additional components and circuitry to enable the lighting device to emit light using electrical energy from a secondary power supply (such as a battery) if the primary power supply (such as a mains supply) is interrupted.
In the event of an electrical power supply failure to a conventional lighting device, the absence of any immediate or sustained ambient light presents numerous safety, welfare, convenience and security concerns to the occupants of any affected public, commercial, industrial or residential buildings and areas. Existing standby or emergency lighting systems typically take the form of a bespoke unit, primarily designed for industrial and commercial environments, which solely function in the event of a power failure (power outage). These existing products typically require dedicated installation, additional wiring and regular maintenance and testing, adding further to purchase and ownership cost. Light is usually only produced in the event of a mains power failure and until either the secondary source is exhausted or primary power is restored, and during that time the user cannot control the light readily, such as to conserve the limited electrical storage capacity when light is not required. Further still, these lighting devices are usually functionally termed “non-maintained” and are only intended to give emergency rather than mainstream illumination when the primary mains power supply is available. Therefore, the associated emergency lighting apparatus is operationally redundant whenever mains power is available and primary lighting is used instead.
Some existing lighting devices are arranged to produce uninterrupted primary illumination from either primary or secondary supplies. These devices are termed “maintained”. In antithesis, lighting devices termed “maintained” are generally intended to produce uninterrupted primary illumination sustained from either mains or secondary electrical storage sources. Maintained devices typically have no switch on supply, hence require permanent mains feed, thus light is usually continuous with the battery being used if the permanent mains feed fails.
The above problems can be solved by combining standard and emergency lighting into one unit that may retro-fit any existing non-emergency light fitting or wiring installation and which may replace or augment any conventional lighting devices powered from the mains power supply.
The present inventor has previously proposed (in GB 2447495) an electric lighting device having circuitry that can detect mains failure and which can provide power to the lighting device from a backup battery provided in or close to the lighting device. One important function of this earlier lighting device is that it is able to distinguish between a failure in the mains power supply and a user controlled removal of the power supply at a light switch. As described in the inventor's earlier GB application, this is achieved by evaluating the impedance across the supply terminals. When there is a mains power failure and the light is switched on, the impedance will be low; whereas when the user has switched off the light at a light switch the impedance will be high.
The present application describes a number of improvements to the lighting device described in the inventor's earlier GB application discussed above.